Robotic Construction Machine Causes Explosion at Fukushima

fukushima remote control construction equipment
A teleoperated robotic excavator similar to the one above caused an oxygen cylinder to explode.

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency.

A teleoperated robotic construction machine accidentally hit an oxygen cylinder at the Fukushima Dai-ichi nuclear plant this Tuesday, causing the cylinder to explode. The unmanned machine, a grapple-equipped excavator fitted with cameras to guide a remote operator, was clearing radioactive debris from the south side of the No. 4 reactor building when a loud explosion was heard around 2:30 p.m.

Despite the loudness of the blast, a Tokyo Electric Power Co. (TEPCO) official told IEEE Spectrum that, “It turned out to be nothing. There was no damage and there was nothing to repair. And the machine is being used again.” He added that the cylinder contained "compressed oxygen, so the noise was loud."

The machine, which the TEPCO official insists is "not a robot," was removing debris flung from the No. 3 reactor building after a hydrogen explosion occurred there on March 14, following the meltdown of the reactor’s fuel rods. Workers are trying to clear the plant of radioactive debris from at least two hydrogen explosions in order to facilitate the set-up of reactor cooling systems and also the transfer of pooled radioactive water from the reactor and turbine buildings to a central radioactive waste disposal facility and other temporary storage.

Because much of the rubble is highly radioactive, TEPCO is employing machines like the remote controlled excavator to remove the contaminated debris. But as this explosion shows, that doesn't mean there are no risks. In fact, an operator controlling a teleoperated robotic machine by relying on cameras rigged to the vehicle may have impaired visual access, making it difficult to spot dangerous objects like oxygen cylinders amid the piles of rubble.

Dr. Robin Murphy, director of the Center for Robot-Assisted Search and Rescue (CRASAR) at Texas A&M University, in College Station, and a world experts on rescue robotics, says that she sees "these kinds of accidents or operator errors all the time." The problem, she explains, is that roboticists are still trying to improve remote presence technologies to allow operators to effectively see and act remotely through a device such as a robot or sensor.

"Many manufacturers think that a certain camera position or multiple cameras will solve the problem of what is sometimes called situation awareness or sensemaking, but this neglects the whole host of subtle, but real, cognitive barriers that arise from working remotely and having perception mediated," she says. Remote operating a robotic system in a constrained environment -- say, an office or in space or underwater -- might actually be easier compared to a disaster-stricken area, which is not well understood and not engineered to make it easy for the robot. "Disasters continue to offer surprises and difficult to model situations."

Image: TEPCO

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